1. Field of the Invention
The present invention relates to a process for preparing a composition comprising a biologically active material. More particularly, the invention relates to a process for producing microparticles comprising a biologically active material and a polymer. The microparticles produced using the process of the present invention can be used to deliver the biologically active material to a human or animal.
2. Description of Related Art
The process of the invention uses a supercritical fluid in the preparation of the microparticles and is particularly suitable for producing microparticles comprising temperature-labile or solvent-labile biologically active materials.
Methods for the production of compositions comprising a biologically active material and a polymer using a supercritical fluid have been reported in the past.
U.S. Pat. No. 5,340,614, WO91/09079 and U.S. Pat. No. 4,598,006 describe methods for providing bioactive material in a biodegradable polymer using supercritical fluids (SCF) to confer porosity during processing of the polymer.
U.S. Pat. No. 5,340,614 describes a method comprising dissolution of additive in a carrier solvent (liquid e.g. water or ethanol). A supercritical fluid (SCF) is then used to allow penetration of the carrier liquid/additive solution into the polymer.
WO91/09079 describes the use of SCF to introduce porosity into biodegradable polymers. If a bioactive material is present, a carrier solvent is required to dissolve the bioactive and to impregnate.
U.S. Pat. No. 4,598,006 describes a method for impregnating a thermoplastic polymer with an impregnation material in a volatile swelling agent at or near supercritical conditions, swelling the polymer and reducing the conditions so that the swelling agent diffuses out.
WO 98/51347 describes a method for the encapsulation of a biologically active material within a biodegradable polymer matrix, without the use of solvents or high temperatures. A supercritical fluid is used to depress the melting or glass transition temperature of the polymer so that the biologically active material can be mixed with the polymer at low temperatures and in the absence of organic or aqueous solvents. This document does not describe ways of optimising the processing of the materials.
WO03/013478 also describes a method of encapsulating an active substance in an interpolymer complex using supercritical fluids. Methods are described involving the dissolution of an interpolymer complex, or components thereof, in a supercritical fluid, or the dissolution of a supercritical fluid in an interpolymer complex. In both these systems an active substance is then encapsulated.
The listing or discussion of an apparently prior-published document in this specification should not necessarily be taken as an acknowledgement that the document is part of the state of the art or is common general knowledge.
The process of the prior art can be associated with problems such as low yield. By this we mean that use of the prior art processes can result in a lower than desirable level of recovery of a product comprising the biologically active material. This can result in a high level of wastage of often expensive biologically active materials.
The solid products of the processes of the prior art often have an irregular shape and/or size and/or an undesirably high surface area. This can make recovery of the product, often resulting in low yields and the use and/or the further processing of the product difficult.